The present invention relates to an apparatus for manufacturing spiral electrode groups for example for a lithium battery, having a construction in which a positive electrode plate and a negative electrode plate are superimposed with a separator therebetween and wound in spiral fashion.
Cylindrical lithium primary batteries or various types of rechargeable batteries of small size and high capacity have long been used as the drive power sources of portable electrical equipment. As improvements in performance and function have been achieved in portable electrical equipment, such batteries are being required to have higher voltage and higher capacity; in order to satisfy such demands, batteries adopting a spiral electrode construction are now widely used, in which a positive electrode plate and a negative electrode plate are superimposed with a separator interposed between these, and wound in spiral form. With such spiral electrode groups for cylindrical batteries of various types, there are important problems to be solved in order to improve productivity and ensure high performance and uniformity of quality. Firstly, the electrode plates must be precisely aligned with each other when wound together in spiral form. Secondly, any excessive tensile force must not be applied to the electrode plates and the separator during the winding of these, or they may be expanded or deformed. On the other hand, the electrode plates and the separator must be wound tightly without any slack portion.
The present inventors have previously proposed an apparatus for manufacturing spiral electrode groups having improved performance and uniformity of quality as described above (see Laid-open Japanese Patent Application No. H9-147878). This apparatus for manufacturing spiral electrode groups will be described with reference to FIG. 10 to FIG. 12. FIG. 10 is a perspective view showing the main structural elements used for manufacturing a spiral electrode group for lithium batteries in the above apparatus. First of all, the concept of forming a strip-shaped electrode group will be described with reference to this Figure. A strip of negative electrode plate 1 is fixed on one surface (the upper surface in the drawing) of a strip of separator 2 by means of non-woven cloth 3 in a predetermined relative position with respect to the separator 2, and a positive electrode plate 8 is overlaid on the other surface (bottom surface in the drawing) of the separator 2. This strip-shaped electrode group is wound up in spiral condition, and its circumference is fixed by means of a circumferential tape 10. Prior to winding up the strip-shaped electrode group, a negative electrode lead portion 4 is mounted on the negative electrode plate 1 and a positive electrode lead portion 9 is mounted on the positive electrode plate 8, respectively.
FIGS. 11A to 11D are diagrammatic perspective views illustrating the sequence of steps of the manufacturing steps in the conventional spiral electrode group manufacturing apparatus. From its central portion S, the separator 2 is divided into a first region Q from one end thereof and a second region P from the other end thereof. The strip-shaped electrode group is formed with the negative electrode plate 1 arranged on the upper surface of one or other of the regions (in this example, the first region Q) in this separator 2 and the positive electrode plate 8 overlaid on the bottom surface thereof, respectively. In the other region P, only the separator 2 is provided.
A winding shaft 11 for winding the aforementioned strip-shaped electrode group is constituted of a winding core 12 and an auxiliary pin 13; winding core 12 is provided in its axial direction with a plurality of grooves (not shown) at its circumference, in the manner of a reamer. First of all, as shown in FIG. 11A, the winding shaft 11 comprising the winding core 12 and the auxiliary pin 13 is made to project towards the central portion S of the strip-shaped electrode group, and is rotated to start winding the strip-shaped electrode group with this central portion S being gripped by the winding core 12 and the auxiliary pin 13. At the time point where this strip-shaped electrode group has been wound a few times, as shown by the arrow in FIG. 11B, the auxiliary pin 13 is withdrawn and removed from the strip-shaped electrode group. After this, as shown in FIG. 11C, the strip-shaped electrode group is wound to completion using only the winding core 12. In this process, winding of the strip-shaped electrode group is performed whilst applying a suitable tension by suction means, to be described. Then, when winding has been completed, as shown in FIG. 11D, a circumferential tape 10 is wound around the electrode group in order to prevent it from coming loose, whereby a spiral electrode group 14 is completed.
FIG. 12 is a vertical cross-sectional view illustrating the major structural portions of the above apparatus for manufacturing spiral electrode groups. A first suction means 17 that holds the first region Q of the strip-shaped electrode group by suction and a second suction means 18 that holds the second region P of the strip-shaped electrode group by suction are arranged on both sides of the winding shaft 11. The winding shaft 11 is, as described in the foregoing, in engagement with the central portion S of the strip-shaped electrode group, and winds the separator from the central portion S thereof as being folded in two. The two suction means 17 and 18 are of identical construction. Specifically, the two suction means 17, 18 are provided with endless belts 19 that respectively attract by vacuum the corresponding regions Q, P of the strip-shaped electrode group by means of a plurality of suction holes (not shown). The endless belts 19 are fed with a desired speed by feed means, in a manner which is responsive to the increased diameter produced by the winding of the strip-shaped electrode group by the winding shaft 11. The first region Q and second region P are thereby displaced towards winding shaft 11 such that a suitable tension acts on the first region Q and the second region P of the strip-shaped electrode group that are respectively held by suction.
The feed means of the endless belt 19 comprises a cam groove 20, a rod 22 having a cam follower 21 provided at its bottom end to engage with the cam groove 20, a pinion 27 that meshes with a rack 24 at the top end of the rod 22 as the rod 22 is moved vertically along a guide 23 in accordance with the shape of the cam groove 20, a drive gear wheel 28 integral with the pinion 27, a transmission gearwheel 29 that meshes with the drive gear wheel 28, and drive rollers 30 that are rotated by the transmission gearwheel 29, causing drive rollers 30 to abut on the endless belts 19, thereby feeding and driving the endless belts 19.
With this spiral electrode group manufacturing apparatus, the first region Q and the second region P of the strip-shaped electrode group, which are respectively held by the respective endless belts 19 of the first suction means 17 and second suction means 18, are displaced towards the winding shaft 11 from both sides by the feed means. Thereby, application of excessive tension to the separator 2 and other elements constituting the strip-shaped electrode group can be prevented. The feed speed of the endless belts 19 is controlled such that this tension is the optimum, so that elongation of the separator 2 and others does not occur and occurrence of winding misalignment of the electrode plates 1, 8 is prevented.
However, it has been ascertained that there is still room for improvement in the manufacturing apparatus for a spiral electrode group as described above. With manufacturing equipment as described above, in the case of manufacturing spiral electrode groups for nickel/cadmium batteries or nickel metal hydride batteries, comparatively good spiral electrode groups can be obtained. This is because, for both of the above types of batteries, the tensile strength of the positive and negative electrode plates is comparatively large and the force of resistance to tension acting during winding of the strip-shaped electrode group is strong and furthermore both of these have an appreciable force of resistance and/or restoring force with respect to elongation of the separator, which is most liable to be subject to the effect of tension. However, when manufacturing spiral electrode groups of, for example, cylindrical lithium primary batteries, the following problems occurred.
The strip-shaped lithium metal foil tape (typically, about 0.14 mm thick and 40 mm wide) constituting the negative electrode plate 1 of a cylindrical lithium primary battery or the like has an extremely small resistance to tension, as a result of which it is readily subject to plastic deformation and easily elongates by about 1 to 2% under slight tension; it suffers a decrease in width or thickness by an amount corresponding to this elongation. It has been confirmed that such change in shape or dimensions of the spiral electrode group caused by elongation of the negative electrode plate 21 is an important cause of deterioration and/or variability of the battery characteristics.
As the strip-shaped electrode group is wound up in spiral fashion about the winding core 12, the diameter of the electrode group gradually increases. While the winding core 12 is rotated at a constant rotational speed, the feed speed of the separator 2 to which the negative electrode plate 1 is fixed and the feed speed of the positive electrode plate 8 must be increased corresponding to the increase in diameter of the electrode group. The speed with which this diameter of the electrode group increases is subtly affected by variations in the thickness of the various materials of the constituent elements of the electrode group, which are different for each battery, and by the tension acting on the separator 2. In this respect, with the manufacturing apparatus as described above, the feed speed of the endless belts 19 i.e. the feed speed of the separator 2 and the positive electrode plate 8 is set by the cam groove 20 of fixed shape, so fine adjustment of the feed speed of the separator 2 etc in accordance with variations of the rate of increase of diameter of the electrode group, which are slightly different for each battery, cannot be made. Consequently, plastic deformation such as elongation or breakage tends to occur in the lithium metal foil tape, which has extremely small resistance to tension.
Attempts have therefore been made to achieve winding of the lithium metal foil tape with the tension set so that scarcely any tension acts thereon, with the object of avoiding occurrence of any elongation at all. However, since strip-shaped lithium metal foil tape has an extremely weak surface and is liable to plastic deformation, if it is subjected to pressure or sliding in a condition in which it is in contact with metallic surfaces of various types, it easily becomes attached to such metallic surfaces. Thus it is extremely difficult to handle. The construction of the above manufacturing apparatus therefore made it impossible, whatever expedient was adopted, to wind a thin strip-shaped lithium metal foil tape securely in a condition without slackness but with no tension acting thereon. The result was that, since the winding-up force of the electrode group 14 was extremely weak, the spiral electrode group 14 that was thus produced was unstable, its shape and dimensions being easily deformed; this gave rise to the new problem of liability to winding misalignment.
Furthermore, in manufacturing equipment as described above, with the object of preventing positional misalignment of the negative electrode plate 1 and the separator 2 on winding of the strip-shaped electrode group and of preventing change of shape due to tension of the negative electrode plate 1, the negative electrode plate 1 is fixed in position to the separator 2 by interposition of non-woven cloth 3. However, since non-woven cloth 3 does not contribute anything to the electricity-generating performance of the battery, material costs are raised by the use of non-woven cloth 3 and the number of manufacturing steps is also increased by the step of sticking on non-woven cloth 3, thereby raising the cost of strip-shaped electrode group 14. Furthermore, since the volume of the spiral electrode group is increased by the non-woven cloth 3, the presence of non-woven cloth 3 constitutes an obstacle to increasing battery capacity.
In view of the above problems of the prior art, an object of the present invention is to provide an apparatus for manufacturing spiral electrode groups whereby a strip-shaped electrode group can be wound while being fed at a variable optimum speed at which no more tension than necessary is applied to the strip-shaped electrode group.
To achieve the above object, the present invention provides a method of manufacturing spiral electrode groups for batteries wherein a strip of positive electrode and a strip of negative electrode are overlaid upon one another with a separator therebetween and wound up in spiral form, comprising the steps of:
providing a strip of separator to a winding core such that the separator is passed through a slit formed in the winding core in an axial direction and is subjected to a predetermined amount of tension;
providing a strip of negative electrode plate made of a metal foil tape to the winding core from a tape suction drum having a rotation axis parallel to the winding core, the tape suction drum being supported rotatably around its axis and is detachably contacted with the winding core under a predetermined pressure;
driving the winding core to rotate, for causing the tape suction drum to rotate synchronously in contact with the winding core by a frictional force acting therebetween, whereby the negative electrode plate held on the tape suction drum is transferred and taken up on the winding core;
attaching a leading end of the negative electrode plate and overlapping same onto the separator at a position predetermined in relation to the separator;
feeding a positive electrode plate toward the winding core;
chucking a leading end of the positive electrode plate together with the separator at a position predetermined in relation to the separator until immediately before the positive electrode plate is taken up on the winding core; and
driving the winding core to further rotate, for winding thereon the negative electrode plate, the separator (2), and the positive electrode plate in an overlapped condition.
According to the present invention, the negative electrode plate is fed toward the winding core from the tape suction drum which is rotated synchronously in contact with the winding core by the frictional force acting therebetween. Since the tape suction drum is detachably pressed against the winding drum, the feed speed of the negative electrode can be automatically increased in accordance with the increase in the diameter of the electrode group that is being wound up, i.e., the electrode plate feeding speed is automatically varied to an optimum value. Therefore, the negative electrode plate is scarcely subjected to any tension and it will not be elongated even though it consists of a thin metallic foil tape. Moreover, the negative electrode plate is positioned with respect to the separator with an adhesive patch, while the positive electrode plate is positioned with respect to the separator by a chucking member, with the result that both electrode plates are precisely aligned in relation to the separator and wound around without any slackness. A spiral electrode group having the required shape can thus be manufactured in a reliable fashion.
In the above invention, it is preferred that the negative electrode plate be fed to the tape suction drum from a tape supply drum which, when contacted with the tape suction drum, rotates synchronously in contact with the tape suction drum, whereby the negative electrode plate held on the tape supply drum is taken up on the tape suction drum, wherein the tape suction drum is provided with a plurality of vacuum suction holes on a circumferential surface thereof, each of the vacuum suction holes being activated in succession to effect vacuum suction holding of the negative electrode plate in synchronism with the taking up of the negative electrode plate on the tape suction drum, and wherein, when the negative electrode plate held on the tape suction drum is transferred and taken up on the winding core, each of the vacuum suction holes cancels the suction holding of the negative electrode plate successively in synchronism with the taking up of the negative electrode plate on the winding core.
In this way, the negative electrode plate can be securely held around the tape suction drum over the entire length without slackness, the suction holding being reliably maintained until the negative electrode plate is completely fed onto the winding core. Smooth and reliable feeding of negative electrode plate is thus accomplished.
Furthermore, to achieve the above object, the present invention provides an apparatus for manufacturing spiral electrode groups for batteries wherein a strip of positive electrode and a strip of negative electrode are overlaid upon one another with a separator therebetween and wound up in spiral form, comprising:
a winding core having a slit formed in the winding core in an axial direction through which a separator is passed;
a tape suction drum for holding by vacuum suction a strip of negative electrode plate made of a metal foil tape on a circumferential surface thereof, having a rotation axis parallel to the winding core, and being supported rotatably around its axis and is detachably contacted with the winding core under a predetermined pressure;
means for feeding a positive electrode plate toward the winding core such as to be overlapped with the separator passing through the slit of the winding core; and
means for driving the winding core to rotate, for causing the tape suction drum to rotate synchronously in contact with the winding core by a frictional force acting between the negative electrode plate and one of the winding core and the separator held thereon, whereby the negative electrode plate held on the tape suction drum is transferred and taken up on the winding core, together with the positive electrode and the separator in overlapped fashion.
According to this apparatus for manufacturing spiral electrode plate groups, the tape suction drum for holding thereon a negative electrode plate by suction and transferring same onto the winding core is rotatably supported and rotated synchronously in contact with the winding core, utilizing the frictional force acting between the two. Accordingly, even though the negative electrode plate is made of a thin metal foil tape, it is subject to practically no tension at all and is not elongated, with the result that a spiral electrode plate of desired shape can reliably be obtained.
In the above invention, it is preferred that a position locating tape, which has an adhesive surface which sticks by itself to the separator held on the winding core at an instant where the tape suction drum has contacted and started to rotate with the winding core, be attached beforehand to a leading end of the negative electrode plate, and that a leading end of the positive electrode plate be chucked by a chucking member as being overlapped with the separator at a predetermined location in relation to the separator, which is passed through the slit in the winding core and subject to a predetermined tension, the chucking member being retracted to release the positive electrode plate immediately before it contacts the winding core or the electrode plate group being wound thereon.
In this way, the occurrence of positional misalignment of the positive electrode plate with respect to the separator immediately after commencement of rotation of the winding core is prevented and positional location is also obtained of the negative electrode plate that is positioned with the separator by the position locating tape. Therefore, the problem experienced with the prior art equipment that it was difficult to wind up both electrode plates precisely in predetermined relative positional relationship can be solved. Also, since the positive electrode plate is fed to the winding core with its feed direction restricted along the feed direction of the separator, winding is achieved with no possibility of positional misalignment with respect to the separator and without any slackness being produced.
The above apparatus of the present invention should preferably further comprise: a rotary support axis around which the tape suction drum is rotatably supported;
a drum support lever which is rotatable around an axis, for supporting at one end thereof the rotary support axis of the tape suction drum; and
biasing means connected at the other end of the drum support lever for biasing the drum support lever in one direction such as to cause the tape suction drum to contact with the winding core under a predetermined pressure.
Thereby, since the tape suction drum is directly pressed onto the electrode group that is being wound onto the winding core by a prescribed pressure by the biasing force of the biasing means, it performs synchronous rotation in contact with this electrode group that is being wound around the winding core while tracking changes in diameter of the electrode group, being always directly pressed, by rotation through the drum support lever, onto the circumferential surface of the electrode group, which is increasing in diameter as it is wound up. Consequently, the speed of rotation of the tape suction drum is automatically increased as the diameter of the electrode group gets larger, even though the speed of rotation of the winding core is always constant, and the feed speed of the negative electrode plate is automatically increased corresponding to the speeding up of the winding up rate resulting from this increase in diameter of the electrode group. Thus variable adjustment to a stable optimum value is always automatically achieved. In this way, even in the step of winding up the electrode group, scarcely any tension is applied to the negative electrode plate made of thin metal foil tape, so there is no possibility of its being elongated.
The above apparatus of the present invention should preferably further comprise: a tape supply drum which holds thereon the negative electrode plate by suction and feeds the negative electrode plate by contacting the tape suction drum and rotates synchronously in contact therewith, wherein
the tape suction drum is formed with a plurality of vacuum suction holes in a predetermined arrangement over an entire surface on which the negative electrode plate is wound, each of the vacuum suction holes being connected, in succession, to a vacuum source to effect vacuum suction holding of the negative electrode plate, concurrently as each of the vacuum suction holes is blocked by the negative electrode plate being taken up on the tape suction drum, and wherein,
when the negative electrode plate held on the tape suction drum is transferred and taken up on the winding core, each of the vacuum suction holes is disconnected from the vacuum source successively, concurrently as the negative electrode plate separates from each of the vacuum suction holes.
Thereby, the plurality of vacuum suction holes that are arranged so as to be capable of applying suction to the entire surface of the negative electrode plate apply vacuum suction to the negative electrode plate successively with optimum timing, with the result that the negative electrode plate is securely held over its entire length without slackness. Since loss of vacuum suction on the negative electrode plate due to intake of atmosphere from the vacuum suction portions that are not blocked by the negative electrode plate cannot occur, the negative electrode plate can always be securely held within a prescribed range irrespective of the winding length of the negative electrode plate, even though a vacuum source of extremely small capacity is employed. When the negative electrode plate is supplied to the winding core, similarly, suction to the negative electrode plate is released with optimum timing and, since the negative electrode plate can be securely held on the tape suction drum until supply thereof to the winding core is completed, supply of the negative electrode plate to the winding core can be achieved in a smooth and reliable fashion.
The tape suction drum may be constituted by:
a rotary support axis;
a rotary section supported rotatably around the rotary support axis, having the plurality of vacuum suction holes formed on an outer circumferential surface thereof, and a guide recess formed on an inner side thereof;
a sliding section supported slidably on the rotary support axis such as to be fitted in the guide recess of the rotary section; and
means for selectively locating the sliding section at a first position predetermined in relation to the rotary section and a second position predetermined in relation to the rotary section, wherein
the sliding section comprises a plurality of first vacuum paths which are successively connected to each of the vacuum suction holes as rotation of the rotary section proceeds in a condition wherein the sliding section is located at the first position, and a plurality of second vacuum paths which are successively disconnected from each of the vacuum suction holes as rotation of the rotary section proceeds in a condition wherein the sliding section is located at the second position, and wherein
the first and second vacuum paths are both connected to a vacuum source through an identical vacuum passage.
Thereby, simply by changing over the sliding section between the first position and the second position, the vacuum suction holes are automatically connected to the vacuum source with the timing with which they are blocked by the negative electrode plate with rotation of the rotary section, and their connection with the vacuum source is automatically cut off with the timing with which the electrode plate is separated by the rotation of the rotary section. Also, since the vacuum circuit can be made common with the exception of the changeover portion of the first and second vacuum paths, the construction can be simplified.
In the above apparatus of the present invention, it is preferred that the rotary section be provided, on an inner surface thereof which faces the sliding section, with a plurality of connection holes arranged facing to each of the plurality of vacuum suction holes in a circumferential direction and spaced apart in an axial direction, the connection holes being in constant communication with the plurality of vacuum suction holes; wherein
the plurality of first vacuum paths comprise a plurality of first grooves arranged such as to face each of the connection holes in the axial direction when the sliding section is located at the first position, the plurality of grooves having gradually decreasing lengths in the circumferential direction; and wherein
the plurality of second vacuum paths comprise a plurality of second grooves arranged such as to face each of the connection holes in the axial direction when the sliding section is located at the second position, the plurality of second grooves having respectively the same lengths as the gradually decreasing lengths of the plurality of first grooves in an inverse arrangement, and being disposed such that each of the first grooves and each of the second grooves are paired and arranged adjacent each other.
The tape suction drum is first located at the reference position, and then is rotated in the same direction in either case in which it takes up thereon the negative electrode plate and in which it feeds the same onto the winding core. In switching over these two operations, it is only necessary to switch over the sliding section between the first position and second position. If a construction were to be adopted in which the tape suction drum were rotated in opposite directions in the case where the negative electrode plate is held and in the case where this is supplied to the winding core, not only would the construction become complicated due to the need to provide two reference positions for positional location of the tape suction drum, but also it would not be possible to stick the position locating tape and/or circumferential tape onto both ends of the negative electrode plate, as a result of which the negative electrode plate and the separator cannot be positioned in relation to each other during the winding.
In the above apparatus of the present invention, it is preferred that the tape suction drum be fixedly located at a reference position at an instant where it is located to contact one of the tape supply drum and the winding core.
Thereby, the tape suction drum commences both winding up of the negative electrode plate onto its circumferential surface and supply of the negative electrode plate onto the winding core from a condition in which it is located in the same reference position. Accordingly, the change of relative position of the rotary section and sliding section accurately corresponds to the angle of rotation of the rotary section, and application of suction and release of suction in respect of the negative electrode plate by the vacuum suction holes can therefore be achieved precisely with the optimum timing just before their blockage by the negative electrode plate and just before their separation therefrom. As a result, no tension at all is applied to the negative electrode plate and suction holding and release can be performed extremely smoothly without production of creases.
As an alternative, the tape suction drum may be constituted by: a rotary support axis;
a rotary section supported rotatably around the rotary support axis, having the plurality of vacuum suction holes formed on an outer circumferential surface thereof;
a stationary section arranged on an inner side of the rotary section, allowing the rotary section to rotate therearound, wherein
the stationary section comprises a plurality of first vacuum paths which are successively connected to each of the vacuum suction holes as rotation of the rotary section proceeds, and a plurality of second vacuum paths which are successively disconnected from each of the vacuum suction holes as rotation of the rotary section proceeds;
a vacuum source to which the plurality of first and second vacuum paths are connected through an identical vacuum passage; and
a switching valve for selectively connecting all of one or other of the plurality of first vacuum paths or second vacuum paths to the vacuum source through the vacuum passage.
By adopting the stationary section instead of the sliding section, the construction can be further simplified, while obtaining the same effects as described above.
The present invention also provides a non-aqueous electrolyte battery comprising a bottomed cylindrical battery case having an upper open end, a spiral electrode group fabricated by the method of manufacturing spiral electrode groups for batteries as described in the foregoing, a non-aqueous liquid electrolyte, and a sealing assembly for hermetically sealing said upper open end of the battery case.
According to this non-aqueous electrolyte battery, since the electrode plate group is wound up without using non-woven cloth as in the prior art, the number of components and manufacturing steps is remarkably decreased, whereby a considerable amount of cost can be reduced, while the battery capacity is increased by the volume previously occupied by the non-woven cloth. Also, since the negative electrode plate is wound up firmly while not being subject to elongation, whereas the positive electrode plate is precisely positioned in relation to the separator, no misalignment occurs and the winding precision is much increased. As a result, the battery according to the present invention has much improved battery performance including discharge capacities.